Although precipitation may be measured by manual or electronic means, electronic instruments that measure rainfall typically do not measure snowfall and vice versa. In fact, frozen precipitation is difficult to measure by electronic instrument. While snowfall may be measured manually by a simple gauge comprising a cylinder having a measurement scale affixed to it, snowfall is difficult to measure by electronic instrument.
Snowfall may be measured electronically by a gauge that melts the snow to water and converts the amount of snow fall to a liquid equivalent. U.S. Pat. No. 6,044,699 discloses such a gauge. The gauge comprises a support structure or an open cylinder, a reservoir for collecting precipitation, means for weighing the reservoir and electronic means for converting the weight measurement to accumulated precipitation. The cylinder includes a small, steeply sloped tapered section to reduce turbulence around the collector. The length of the collector assembly is minimized to reduce area for frozen precipitation to accumulate. The cylinder is heated sufficiently to raise the temperature of the collector assembly so that frozen precipitation is melted. U.S. Pat. No. 5,744,711 discloses a winter precipitation measuring system for quantifying the precipitation rate of winter precipitation that attempts to overcome problems associated with the weighing type snow gauge as disclosed in the '699 patent. The system includes an elongated tube, a thermal plate within the tube and an apparatus for maintaining the thermal plate at a substantially constant temperature relative to a reference plate and for determining a precipitation rate in response to the difference in power consumption required to maintain the thermal plate at a substantially constant temperature. These snow gauges do not provide the amount of snow fall in depth nor do they measure the “wetness” or density of the snow which would be useful in areas where snow blowing equipment is used.
Other patents disclose devices for detecting frozen precipitation and differentiating between rain and frozen precipitation. For example, U.S. Pat. No. 4,656,333 discloses a moisture sensing detector of snow, sleet, ice and rain. The detector includes a sensing probe and coacting control circuitry for receiving the moisture signal from the probe and actuating associated equipment. The probe includes electrically charged electrodes spaced apart by a small distance. Any moisture bridging the gap completes a circuit between the electrodes. This device only detects moisture or precipitation but does not measure the amount or rate of precipitation. U.S. Pat. No. 5,557,040 discloses a method and apparatus for precipitation detection and differentiation. A direct backscatter technique provides for the detection of precipitation in a measuring volume. A source light beam is projected into the measuring volume. Light in the volume, including source light scattered from any precipitation within the volume, is collected and detected. A signal is generated corresponding to the detected light. This signal is used to determine whether precipitation is present in the measuring volume. The light scattered from precipitation within the measuring volume may also be used to differentiate between types of particles such as rain or snow. Rain or snow can be differentiated based on whether the transmitted light changed from its original polarization state. Thus, while the '040 patent discloses an apparatus and method for detecting the presence of precipitation and differentiating between rain and snow, the patent does not disclose a method or apparatus for measuring the amount of frozen precipitation that has fallen or the rate at which frozen precipitation falls.
U.S. Pat. Nos. 3,942,762 and 5,138,301 disclose a well-known type of rain gauge comprising a stationary reception funnel having a water discharge nozzle at its lower end. A receptacle having two symmetrical compartments of a known volume is located below the discharge nozzle. As one compartment fills with water it rocks in one direction to dump the water and to allow the other compartment to fill with water. A switch that is affixed to the receptacle is opened and closed by the rocking motion. From the cross-sectional area of the input of the funnel and from the amount of water which causes the receptacle to rock, the amount of precipitation can be determined by counting the number of times the switch has opened and closed for a given period of time. This instrument cannot, however, measure snowfall.
U.S. Pat. No. 4,305,280 discloses a rainfall intensity sensor that measures the rate of rainfall or snowfall by determining the electrical power required to evaporate water or snow as it contacts an exposed sensor. A number of assumptions are made in order to correlate the electrical power used by the device with the rate of rainfall or snowfall which may affect the accuracy of this device. Moreover, the device disclosed in the '280 patent does not determine the total amount of rain or snow (i.e., in inches) that fallen over a certain period of time or the density of the snowfall.
A snow gauge device which uses an infrared proximity sensor is disclosed at the website www.howmuchsnow.com/snow/. The infrared proximity sensor, such as an infrared triangulation measurement sensor, comprises a light detector and light emitter that are adjacent to each other. The sensor is attached near the top of a vertical post that is mounted on a base board so that the light emitter and light detector are pointed downwardly toward the base at an angle. As snow accumulates on the base, the infrared LED emits a beam of light, which is reflected off of the snow and back to the detector, which is a linear array. The location that the reflected light strikes the linear array is related to the distance that the snow is from the sensor. An ultrasonic sensor may be used but must be mounted perpendicular to the snow surface because the ultrasonic beam is wide and hard to focus on a surface. This snow gauge device may be limited to the height of snowfall that it can measure and is not capable of measuring rainfall.
With the advance of electronics, electronic weather stations that provide wind speed temperature, humidity, pressure, and rainfall have become popular, particularly for residential use. Because of the difficulty of automating the measurement of frozen precipitation, these weather stations do not provide measurements of frozen precipitation, particularly snow. The prior art snow gauges are not suitable for electronic weather stations made for residential use. These prior art gauges are expensive or do not provide electronic display of the amount of frozen precipitation that has fallen in a given time period. Instead, the prior art snow gauges provide the amount of frozen precipitation in liquid equivalent or the amount of snow must be manually read from a scale on the snow gauge.
What is needed is a simple, relatively inexpensive instrument to measure, display, and record amounts of precipitation whether rain, snow, sleet or frozen rain. What is particularly needed is an instrument that measures frozen precipitation in, for example, inches—not liquid equivalent. What is also needed is an instrument that measures both liquid and frozen precipitation and records and displays the rate of the falling precipitation. What is further needed is an instrument that measures, records and displays the rate of the precipitation. What is also needed is an instrument that determines the density of frozen precipitation, particularly snow, so that snow blowing equipment can be adjusted and operated for optimum use.